Text Messages and Voicemails------Where are they actually stored?

Several  parts to the question.  Do voicemails and text messages reside only on my device?  Or are they also on a server someplace in the Xfinity or Verizon system?  I know that Xfinity leases tower time from Verizon, so that is why I include it in the question.

If I delete a text or voicemail, is it in fact really gone?  Or does it still exist someplace in the Xfinity/Verizon system?

Also, how far back are texts or voicemails supposed to exist until deleted by me?   I became an Xfinity mobile customer back in February.  The device is a Samsung A36 5g.  My "Expert" status is mostly confined to helping people with email.  So any help here is appreciated.